Condition responsive control device with capacity for independent adjustment of control points and transducer therefor

ABSTRACT

A control device having a pressure sensing element coupled to a balance plate. The balance plate, in turn, is coupled to a microswitch by an actuating rod. Variations in pressure displace the sensing element which, in turn, pivotally displaces the balance plate sequentially about first and second axes. A pair of springs are coupled to the balance plate by bosses which extend different distances from the balance plate. The bosses facilitate use of identical springs and adjusting members in a control device where the differential between control points is fully adjustable. The control device has a housing including upper and lower sections, the upper section having a microswitch associated therewith, the lower section having the balance plate and associated elements disposed therein. A recessed space at the exterior of the housing is defined by the upper and lower housing sections. The adjusting members for the springs extend into the recessed space so as to be readily accessible from the exterior of the housing. The control device includes a detachable pressure transducer which facilitates conversion of the control device from one application to another.

United States Patent Otto et al.

Oct. 7, 1975 THEREFOR [73] Assignee: Automatic Switch Company,

Florham Park, NJ.

[22] Filed: Dec. 6, 1973 [21] Appl. No.: 422,432

[52] US. Cl. 200/83 S; 200/286; 73/406 [51] Int. Cl.'- I-IOll-I 35/34 [58] Field of Search 200/18, 153 T, 81.4, 83 J, 200/83 R, 83 P, 83 S, 83 SA, 83 T, 286; 340/229, 240; 73/406, 410, 419; 92/95, 96, 101, 130

[56] References Cited UNITED STATES PATENTS 3,210,486 10/1965 Holzer 200/81 R 3,390,242 6/1968 Koepkc... 200/153 V 3,393,612 7/1968 Gorgens. 73/406 3,419,693 12/1968 Gould 200/83 .1 3,490,342 1/1970 Reis.... 92/130 3,594,521 7/1971 Roll 200/83 P 3,786,212 1/1974 Weber 200/83 R Primary Examiner-Gerald P. Tolin Attorney, Agent, or FirmBacon & Thomas [5 7 ABSTRACT A control device having a pressure sensing element coupled to a balance plate. The balance plate, in turn, is coupled to a microswitch by an actuating rod. Variations in pressure displace the sensing element which, in turn, pivotally displaces the balance plate sequentially about first and second axes. A pair of springs are coupled to the balance plate by bosses which extend different distances from the balance plate. The bosses facilitate use of identical springs and adjusting members in a control device where the differential between control points is fully adjustable. The control device has a housing including upper and lower sections, the upper section having a microswitch associated therewith, the lower section having the balance plate and associated elements disposed therein. A recessed space at the exterior of the housing is defined by the upper and lower housing sections. The adjusting members for the springs extend into the recessed space so as to be readily accessible from the exterior of the housing. The control device includes a detachable pressure transducer which facilitates conversion of the control device from one application to another.

22 Claims, 20 Drawing Figures US. Patent Oct. 7,1975 Sheet 3 of5 3,911,238

US. Patent Oct. 7,1975 SheetS of5 3,911,238

CONDITION RESPONSIVE CONTROL DEVICE WITH CAPACITY FOR INDEPENDENT ADJUSTMENT OF CONTROL POINTS AND TRANSDUCER THEREFOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to devices which produce control signals in response to condition changes. Preferably, the invention is embodied by a pressure switch, that is, a device producing an electrical signal in response to changes in pressure Nevertheless, the invention may also be embodied by devices which measure conditions other than pressure and which produce signals other than electrical. For instance, the invention could be embodied by a temperature responsive device or a vacuum responsive device. By the same token, the invention could be embodied by a device which produces fluid or fluidic control signals in response to variations in a given condition.

In particular, the device of the-present invention, in certain of its aspects, falls within a class of condition responsive devices which can be described as alternating fulcrum or alternating axis devices. In this type of device, a pressure sensing element is coupled to a balance plate or balance beam which pivots, alternately, about a pair of fulcrums or axes. Pivotal movements about the different axes effect actuation of the device into different control modes. Examples of alternating fulcrum and alternating axis control devices are found in U.S. Pat. Nos. 2,284,940; 2,266,144 and 2,274,119, all to A.E. Baak; U.S. Pat. No. 2,766,349 to H. F. Hamburg and U.S. Pat. No. 3,210,486 to W; Holzer.

The present invention relates specifically to improvements in the construction of control devices of the foregoing type. For instance,-the balance plate of the present invention has an improved and simplified construction, which, in turn, permits simplification and improvement in the arrangement of the adjusting members and biasing springs which act on the balance plate. The invention also relates toimprovements in the construction of condition responsive devices in general. For instance, the device of the invention has an improved housing construction which facilitates access to the adjusting members and an improved pressure transducer assembly which makes the control device adaptable to different pressure ranges.

2. Description of the Prior Art In the foregoing U.S. Patents to A. E. Baak, a balance beam is biased against movement by a pair of adjustable springs which are adjusted to exert different biases. Whenthe pressure sensing element moves the balance beam against the biasing force of these springs, the spring adjusted to exert the weaker bias will yield first, permitting movement of the balance beam about one fulcrum. As pressure increases, the spring adjusted to exert the heavier bias will yield, permitting movement of the beam about the other axis. To provide proper operation of the device, one spring should always act as the heavier spring and the other should always act as the lighter spring. That is, the functions of the two springs cannot be reversed. Yet, in the Baak devices and in other known devices, reversing may occur by improper adjustment. Reversing, in turn, causes malfunctioning of the control device and, in some cases, this may result in damage to the device.

A solution to the foregoing problem is provided in a copending application of Ernesto J. Weber, Ser. No. 236,732, filed Mar. 21, 1972, now allowed, which application is hereby incorporated into the present disclosure by reference. Each of the springs of the control device of the aforesaid Weber application has one adjusting member associated therewith, each adjusting member being of a different configuration than the other. The two adjusting members have an interlock between them to prevent reversal of their relative positions. Specifically, the two adjusting members cooperate with one another in such a way that one is always disposed above the other thereby assuring that the spring associated with the higher adjusting member always has a lighter bias than the other spring, and vice versa. The interlock is effected by overlap of outwardly extending rims on the adjusting members. However, excessive vertical staggering of the adjusting members due to overlap of the rims must be avoided or compensated for if full adjustability of the differential between control points is desired. Heretofore, it has not been known how to eliminate the undesirable effects of vertical staggering and yet take advantage of the simplicity and economy of using identical springs and adjusting members.

In the device disclosed in the foregoing Weber application, the driving heads of the adjusting members are disposed above the top closure of the housing. The microswitch, which, in practice, is and must be enclosed by a cover, has a similar disposition with respect to the housing. Thus, the driving heads of the adjusting members are enclosed by a cover which must be removed in order to effect adjustment of the biasing springs. Particularly in situations where an explosion-proof cover is used, the need to remove the cover to effect adjustment of the control device is inconvenient.

U.S. Pat. No. 3,393,612 to J. E. Gorgens et al. further illustrates the problem of locating the head of an adjusting member within a cover or housing for a microswitch. Again, at least part of the cover must be removed to effect adjustment of the biasing spring.

The Gorgens et al. patent is also of interest with regard to its disclosure of interchangeable pressure transducer elements to effect conversion of a control device from one operable in a given pressure range to one operable in a different pressure range. It is to be observed, however, that the only truly interchangeable part in the Gorgens et al patent is a combined piston-cylinder element. When it is desired to convert the device from one pressure range to another, a considerable amount of disassembly and reassembly is required. Specifically, each-time a conversion is made, it is still necessary to remove and reinstall the diaphragm and O-ring.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a control device of the alternating axis type, wherein both the overall control device and, particularly, the balance device therefor, are of improved and simplified construction embodying relatively few parts and which can be constructed at a relatively low cost.

It is another object of the invention to provide a control device having identical springs acting on a balance plate, having identical adjusting members for the springs, and wherein full adjustability of the differential between biasing control points is possible.

It is a further object of the invention to provide a balance device for an alternating axis pressure switch or the like wherein the elements of the balance device, namely, (l) abalance plate, (2) bosses for connecting the biasing springs to the balance plate, (3) certain stop elements for defining the pivotal axis about which the balance plate pivots, and (4) certain guide elements, are all integrally formed with one another.

It is an additional object of the invention to provide a balance device with an improved guide arrangement therefor.

It is also an object of the invention to provide a control device wherein access to the driving heads of the adjusting members is facilitated.

It is a further object of the invention .to provide adjusting members which also serve as guides for the associated biasing springs.

It is another object of the invention to provide a control device with a detachable, interchangeable pressure transducer subassembly whereby conversion of the control device to sense different ranges of pressuress is facilitated.

It is a related object of the invention to provide an interchangeable transducer subassembly with means for holding the elements of the subassembly together when the subassembly is detached from the main housing.

It is another related object of the invention to provide means for retaining elements of the control device within the main housing thereof when the transducer subassembly is detached.

It is yet another object of the invention to provide a pressure transducer subassembly with a bonnet, the bonnet having a plurality of means for coupling different sized pressure sensing devices therein (one at a time) so that the size of the sensing device can be made comensurate with the pressure range to be sensed.

SUMMARY OF THE INVENTION The present invention overcomes the shortcomings of the prior art and achieves the foregoing objects by providing a control device having a balance plate with a pair of bosses on one side thereof, one boss extending a greater distance from the plate than the other boss. A pair'of biasing means, each of which has an adjusting member associated therewith, is connected to the balance plate via the bosses. Overlapping rims on the adjusting members provide a simple interlock mechanism to prevent reversal in the functioning of the biasing means and balance plate. This type of interlock, however, effects a minimum vertical staggering of the adjusting members, which staggering must be compensated for if full adjustability of the differential between actuation points is desired. The vertically staggered bosses provide the needed compensation and also facilitate the use of identical biasing means and identical adjusting members.

A plurality of stop means cooperate with the balance plate to define a pair of axes about which the balance plate pivots in response to variations in a sensed condition. The balance plate has a guide projection thereon, the projection having the configuration of a prism with triangular end faces. The prism-shaped guide projection cooperates with a similarly shaped opening in a stationary guide member. The guide projection is so positioned with respect to the balance plate as to provide a maximum guiding effectiveness, yet a minimum resistance to alternating pivotal movements of the balance plate. Furthermore, the guide projection serves to locate the balance plate at the proper angular position in the housing.

The balance plate, the bosses, the guide projection and certain elements of the stop means are embodied by a unitary molded piece which, preferably, is composed of plastic. This piece is referred to generally as the balance device. A spherical member composed of a material harder than the material of the balance means (preferably steel), is molded into the guide projection to act as a bearing member at the joint between the balance device and the transducer assembly.

The housing is divided at least into upper and lower sections which sections define a recessed space therebetween. The balance plate and the springs which act on the balance plate are located in the lower section of the housing. An actuating rod extends from the balance plate to a microswitch carried by the upper housing section. The adjusting members for the biasing springs are disposed partially within the lower housing section but extend therefrom into the recessed space. The driving heads of the adjusting members are disposed entirely in the recessed space so that the adjusting members may be readily adjusted from the exterior of the housing. Each adjusting member has an elongated hollow body enclosing the major portion of at least one spring biasing means. Thus, each adjusting member serves as a guide means for its associated spring.

The control device of the present invention includes an interchangeable transducer assembly detachably secured to the main housing. The construction and arrangement is such that one transducer assembly may readily be substituted for another to adapt the control device for operation in different pressure ranges; The complete transducer assembly is constructed so that the elements thereof form a single unit which is held together even when the assembly is detached from the main housing. A set of eyelets in the assembly serve the dual purpose of holding the elements of the assembly together at all times while providing a bore for attachment of the transducer assembly to the main housing. Changing transducer assemblies is facilitated by the fact that, even when the assembly is detached, the components within the main housing are retained therewithin.

The transducer assembly includes a bonnet which housess a sensing device therein. The bonnet has a plu- 'rality of means for interchangeably coupling sensing devices of different forms and sizes therein. When a particular range of low pressures is to be sensed, a sensingdevice, which is of an appropriate size and form therefor, is coupled to the bonnet by a first coupling means. When a particular range of medium pressures is to be sensed, a sensing device of a different size and form is coupled to the same bonnet, or a different bonnet of the same configuration, by a second coupling means. Finally, when a particular range of high pressures is to be sensed, another, different sensing device may be coupled to the bonnet by a third coupling means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of the control device of the present invention;

FIG. 2 is an enlarged vertical sectional view through the control device of FIG. 1 showing, attached to the main housing, a transducer assembly for sensing a range of medium pressures;

FIG. 3 is a transverse vertical sectional view, taken substantially on the line 33 of FIG. 2 and showing an explosion proof switch cover in place of the general purpose cover shown in FIGS. 1 and 2;

FIG. 4 is an enlarged, fragmentary, vertical sectional view of that region of the device of FIG. 2 disposed in the vicinity of the upper end of the switch actuating rod;

FIG. 5 is an enlarged, horizontal sectional view taken on the line 55 of FIG. 1;

FIG. 6 is a staggered horizontal sectional view taken on the line 66 of FIG. 1;

FIG. 7 is a horizontal sectional view, on a smaller scale, taken on the line 7-7 of FIG. 2;

FIG. 8 is a horizontal sectional view, on a smaller scale, taken on the line 88 of FIG. 2;

FIG. 9 is a fragmentary vertical sectional view, taken on the line 99 of FIG. 8, but showing, attached to the main housing, a transducer assembly for sensing a range of low pressures;

FIG. 10 is a fragmentary vertical sectional view, similar to FIG. 9, but showing, attached to the main housing, a transducer assembly for sensing a range of high pressures.

FIG. 11 is a perspective view of the upper stop plate of the control device of FIG. 2;

FIG. 12 is a perspective view of the balance device of the control device of FIG. 2;

FIG. 13 is a perspective view of the spacer ring of the control device of FIG. 2;

FIG. 14 is a perspective view of the guide member of the control device of FIG. 2;

FIG. 15 is a perspective view of the lower stop plate of the control device of FIG. 2;

FIG. 16 is a perspective view of a cylinder member for the medium pressure transducer assembly of the control device of FIG. 2;

FIG. 17 is a perspective view of a cylinder member for the low pressure transducer assembly according to FIG. 9;

FIGS. 18 and 19 are fragmentary sectional views of the lower part of the control device of FIG. 2, but showing various displaceable elements in different positions;

FIG. 20 is an enlarged, fragmentary, vertical sectional view of that region of the device of FIG. 2 where the rims of the adjusting members overlap.

DETAILED DESCRIPTION OF THE DRAWING In the following description and in the drawing, like reference characters, when used in connection with different figures of the drawing, refer to like elements and/or features.

General Construction Referring to FIGS. 1, 2 and 3 there is shown a control device having a main housing which is referred to generally by reference numeral 10. The housing has an upper section 12 and a lower section 14, both sections being of generally cylindrical configuration, and being joined to one another by a connecting section 16. As is apparent from the drawing, the upper section 12, when considered with its associated cover (to be described hereafter), forms an upper enclosure. As is also apparent, lower section 14 forms a separate lower enclosure. The upper and lower cylindrically shaped sections 12, 14 are aligned with one another on a common central axis, but the connecting section 16 is offset from this axis and is disposed entirely to one side thereof. The main housing 10 has a unitary construction; that is, the upper section 10, lower section 14 and connecting section 16 are all integrally joined together. The upper and lower sections l2, 14 are spaced from one another a substantial vertical distance, which distance is at least one-third of the axial length of the entire lower section 14. By virtue of this vertical spacing and the offset location of the connecting section 16, a recessed space 18 is defined between the upper section 12, lower section 14 and connecting section 16 (see FIG. 3).

A transducer assembly, generally referred to by reference numeral 20, is detachably secured to the lowermost end of the main housing 10 in contiguous relationship with the lower section 14 thereof. Transducer assembly 20 includes a two-piece bonnet 22, one piece of which is an end closure 24, the other piece of which is a bonnet ring 26 which receives the end closure 24 therewithin and which clamps the end closure to the main housing 10. This two'piece bonnet can also be made as one piece.

Within the bonnet 22, an O-ring 28 engages the lower side 30 of a diaphragm 32. In the particular medium pressure transducer arrangement of FIGS. 2 and 3, a radially outward portion of the upper side 34 of the diaphragm engages a cylinder member 36 which is secured in the bonnet. O-ring 28 urges the diaphragm 32 into a tight, face-to-face engagement with the cylinder member 36 and seals the diaphragm with respect to the bonnet 22. With this arrangement, a pressure-tight, sensing chamber 38 is defined between the diaphragm 32, O-ring 28 and bonnet 22. When the device of the invention is to be used as a pressure switch, fluid under pressure is admitted into chamber 38 via connecting port 40 in the end closure 24 of bonnet 22.

A central portion of the upper side 34 of diaphragm 32 engages a piston 42 in face-to-face relationship therewith. Displacements of the diaphragm, effected by variations of pressure in chamber 38, are transferred directly to the piston 42 which is displaceable within cylinder 36. The piston, in turn, engages a displaceable balance device 44 which is disposed in the main housing 10.

The structural details of the balance device can be seen most readily in FIG. 12 As illustrated, a flat, plate-like member forms the major portion of the balance device. This member is designated by reference character 46 and referred to hereafter as the balance plate.

The balance plate has a generally triangular configuration which, more precisely, may be defined as the general configuration of a prism having end faces in the form of equilateral triangles. On the lower side of the balance plate 46, there is disposed a guide projection 48. The guide projection 48 also has the configuration of a prism with end faces in the form of equilateral triangles. Three sides 48a, 48b, and 48c (which act as guide surfaces) on the guide projection 48 (see FIG. 8) correspond with the legs of the aforesaid equilateral triangles.

As will be readily apparent from the broken line portions of FIG. 7, the prism-shaped guide projection 48 and prism-shaped balance plate have opposite angular dispositions relative to one another. Specifically, the relative angular dispositions are such that the two prism-shaped elements are 60 out of phase with one another, whereby a corner of one corresponds to the midpoint of a side of the other and vice versa.

A guide member 49 (see FIG. 14) including a guide opening 50, is disposed in the lower housing section 14 in a position immediately below the balance plate 46. The configuration of the guide opening 50 corresponds with that of the guide projection 48 and, indeed, the guide projection displaceably fits within guide opening 50 to thereby guide the balance device through its displacements. The guide member 49 is composed of a flexible plastic material which, preferably, will be a plastic material sold under the trademark Mylar.

The balance device 44 includes a plurality of protrusions 51, 52, 54, 56, 58 extending from the upper and lower surfaces of the balance plate 46. Each of the protrusions 51, 52, 54, 56, 58 have a semi-spherical configuration, that is, the protrusions take the form of truncated spheres.

Protrusions 51, 52 which are disposed on the lower surface of the balance plate, cooperate with a lower stop plate 60 (see FIG. 11) to define one axis, namely, axis A (see FIGS. 7 and 12), about which the balance device pivots during operation. Likewise, protrusions 54, 56 on the upper side of the balance plate cooperate with an upper stop plate 62 (see FIG. 15) to define another axis, namely, axis B, about which the balance plate also pivots during operation.

Protrusions 51, 54 are vertically aligned with one another as is evident in FIG. 12. These protrusions, which are referred to hereafter as the upper and lower pivotal protrusions, may simultaneously engage the upper and lower stop plates 60, 62 to suspend the balance plate in the lower section of the housing. In this regard, the relationship of elements is best illustrated in FIG. 3. It is possible that, in actual practice, a slight clearance may exist between the upper and lower pivotal protrusions 51, 54, on the one hand, and the cooperating upper and lower stop plates 60, 62, on the other hand. Thus, strictly speaking, both protrusions may not actually engage the upper and lower stop plates simultaneously. However, at least one of the pivotal protrusions 51, 52 will engage one of the stop plates 60, 62 at all times.

The alternating pivotal movement of a balance plate in a control device has been described in the aforementioned application of Ernesto J. Weber and the particular operating movements of the present balance device 44 will be described in a later section herein. However, for purposes of understanding the structural arrangement of elements, it is helpful to now refer briefly to the movement of the balance device 44. In this regard, the alternating pivotal movement is best understood by reference to FIGS. 2, I8 and 19.

When the balance device is in the low pressure position, illustrated in FIG. 18, all the protrusions on the lower side thereof, namely, protrusions 51, 52 and 58, will engage the lower stop plate 60. of these three protrusions, protrusion 58, which shall be referred to the rest protrusion, is substantially smaller than the others. This is so because rest protrusion 58 simply provides an abutment for the balance plate when it is in its lowermost position. Thus, unlike protrusions 51, 52, 54, 56, the rest protrusion 58 does not serve as a bearing which defines axes about which the balance device pivots.

As the balance device moves from the low pressure position of FIG. 18 to the middle position of FIG. 19, it pivots about an axis A (FIGS. 7 and 12) which is defined by the bearing points of protrusions 51 and 52 on the upper surface of lower stop plate 60. Because it partially defines the axis about which the balance device pivots under the influence of low pressures, protrusion 52 shall be referred to as the low pressure protrusion. from As can be best seen from FIGS. 11, 14 and 15, the protrusions 51, 52 and 58 on the lower side of the balance plate directly engage lower stop plate 60 rather than the guide member 49. This result is attained by providing a set of three equally spaced holes 64 through the guide member. The holes 64 are arranged to correspond with the positions of protrusions 51, 52 and 58 on the balance plate; and, becuase of these holes, the upper surface of stop plate 60 is exposed to the lower surface of the balance device in the regions of the aforesaid three protrusions.

It will be understood that, in FIG. 12, for purposes of more fully showing details of construction, the balance device 44 is rotatably misaligned from the other elements shown thereabove and therebelow in FIGS. 11 and 13-17. With this exception, however, the parts shown in FIGS. 1ll7 are disposed as they would be if assembled. Rotating the balance device of FIG. 12 approximately 90 in a counterclockwise direction, would properly align it with the elements of FIGS. 11 and l3l7.

When the balance device moves from the middle position of FIG. 19 to the high pressure position of FIG. 2, it pivots about an axis B defined by the bearing points of protrusions 54 and 56 on the lower surface of the upper stop plate 62. For obvious reasons, protrusion 56 shall be referred to hereafter as the high pressure protrusion.

A pair of bosses 66, 68 extend different distances from the upper surface of the balance plate 46. Boss 66, is generally of the same size and convex configuration as protrusions 51, 52, 54, 56. Boss 68, however, is of a more elongated configuration, whereby only the outer, free end has a convex shape. Preferably, boss 68 extends from the balance plate a distance which is more than twice the distance which boss 66 extends therefrom. In an actual working embodiment of the present device, boss 66 extends approximately 0.07 inches from the upper surface of the balance plate, while boss 68 extends an additional 0. [0 inches therefrom (i.e., approximately 0.17 inches therefrom).

The balance plate 46, guide projection 48, convex protrusions 51, 52, 54, 56, 58 and bosses 66, 68 are all integrally formed into a unitary piece which is referred to as the balance device 44. The balance device 44 is formed of a molded plastic material, which preferably, is a material sold under the trademark Fiberite, specifically, Fiberite PM 4005.

A steel ball 70 is molded w thin the balance device 44 so that part of the ball protrudes downwardly from the guide projection 48. Guide projection 48 extends downwardly through opening 71 in the lower stop plate 60 to permit ball 70 to engage the upper surface of piston 42 and to act as a bearing for transferring motive forces of the piston to the balance device 44.

The upper and lower stop plates 62, 60, between which the balance device 44 is disposed, are held in spaced relationship by spacer ring 72. Guide member 49 is clamped into position between the spacer ring 72 and lower stop plate 60. The unit consisting of the balance device 44, guide member 49, stop plates 60, 62 and spacer ring 72 can be considered as the actuating unit of the control device. This actuating unit is independently secured within the lower housing section 14 by a set of elongated screw fasteners 74, each of which extends through bothstop plates and into the housing.

Disposed within the lower housing section 14 is a pair of compression coil springs 76, 78 which act on the balance device through spring retainers 80, 82. The upper ends of the springs are coupled to identical, elongated, hollow adjusting members 84, 86, each of which is adapted to selectively vary the biasing force of its associated spring. Cut-outs 83 in the upper stop plate 62 permit springs 76, 78 to pass therethrough. Although springs 76, 78 are substantially identical, one of the springs, namely spring 76, is generally adjusted to exert a lesser biasing force than the other spring 78. Thus, spring 76 shall be referred to as the low pressure spring and spring 78 shall be referred to as the high pressure spring.

Spring retainers 80, 82 are of a unitary, molded construction and are preferably formed from a material sold under the trademark Celcon, specifically Celcon M90-04. Spring retainer 80 includes thereon a concave recess 88 which mates with a convex free end of the elongated boss 68 of the balance device 44 thereby coupling the low pressure spring 76 with the balance device. Likewise, spring retainer 82 includes a concave recess 90 which mates with the convex surface of the smaller boss 66 to couple the high pressure spring 78 to the balance device.

Adjusting members 84, 86 are externally threaded along most of their length. A pair of internally threaded openings 92, 94, disposed side-by-side in a top wall 96 of the lower housing portion 12, threadably couples the adjusting members 84, 86 to the housing so that the adjusting members extend perpendicularly through the top wall 96. In all positions of adjustment, the lower ends of both adjusting members 84, 86 are disposed interiorly of the lower housing section 14 while the upper ends of both adjusting members are disposed exteriorly of the lower housing section and within the recessed space 18. The size of recessed space 18 is further defined by the fact that its vertical dimension (i.e., the distance between the upper and lower housing sections 12, 14) is at least one-half the length of an adjusting member 84, 86 and at least one third the vertical dimension of that part of the control device consisting of the lower housing section 14 and transducer subassembly 20.

Each of the coil springs 76, 78 is partially enclosed within the hollow interior of its associated adjusting member. The lengthof each adjusting member with'respect to its associated spring is such that each adjusting member encloses at least half the length of the spring in all positions of adjustment. By enclosing springs 76, 78 in this fashion, the adjusting members 84, 86 act as guides to prevent buckling of the springs.

At the lower end of adjusting member 84, there is disposed a radially outwardly extending rim 98. Likewise,

adjusting member.86 includes an identical rim 99 at its lower end. Rims 98, 99 act as stops to define the limits of adjustment. Thus, when adjusting member 84 is threadably advanced upwardly into a position of adjustment (as shown in FIG. 2) wherein low pressure spring 76 will exert its lowest bias, rim 98 engages top wall 96 of the housing to prevent further upward movement of adjusting member 84. Likewise, when adjusting member 86 is threadably advanced downwardly into a position of adjustment (as also shown in FIG. 2) wherein high pressure spring 78 will exert its greatest bias, rim 99 engages the upper stop plate 62 to prevent further downward movement of adjusting member 86.

As best seen in FIG. 20, the adjusting members are so arranged that the rims 98, 99 overlap each other. This makes it impossible to adjust the low pressure spring 76 to exert a biasing force which is greater than the biasing force of the high pressure spring, and vice versa. Specifically, adjusting member 84 cannot be advanced to a position below that of adjusting member 86 due to interference of the respective rims. Likewise, adjusting member 84 cannot be advanced to a position above that of adjusting member 86 for the same reason.

Ordinarily, the thicknesses t and (see FIG. 20) of the two overlapping rims 98, 99 would create a given minimum difference in the biasing forces of the respective springs 76, 78. That is, because of the thicknesses of the rims, one adjusting member must always be vertically staggered at least a given minimum distance with respect to the other. The vertical staggering would ordinarily result in a substantial, given, minimum difference in the biasing forces of the respective springs, and this is particularly true where, as here, identical springs and adjusting members are used. The foregoing minimum difference in biasing forces is actually a function of the sum of one half the thickness of each rim, i.e., M t +t (see FIG. 20), assuming that identical springs and adjusting members are used. This sum corresponds to the distance d of FIG. 20.

The foregoing minimum difference in biasing forces, unless eliminated or compensated for, would limit the adjustability of the control device. That is, the given minimum difference in the biasing forces of the springs would result in a given minimum differential between the actuation points of the control device. Where, as here, identical adjusting members and springs are used, and where practicable thicknesses t are set for the rims of the adjusting members, the resulting minimum differential between control points would eliminate an important portion of a full range of adjustability. Specifically, it would eliminate the capability for adjusting the springs to provide very small differentials between control points.

The present invention solves this problem with an extremely simple structural feature, namely, the aforementioned bosses 66, 68 which extend different distances from the balance plate 46. The difference between the distances which the bosses extend from the balance plate 46 corresponds with the minimum vertical staggering of the adjusting members caused by the overlapping rims thereon. The bosses, in effect, provide a vertical staggering in the points of connection of the springs to the balance device, the latter vertical staggering being precisely the reverse of the former minimum vertical staggering of the adjusting members.

Because of the different heights of the bosses 66, 68, the springs 76, 78 will exert approximately equal biases when the adjusting members are moved into their positions of minimum vertical staggering (see FIG. 20).

Here, there will be nearly a zero differential between control points. Of course, it is possible to adjust the springs to effect other differentials, including a range of very small differentials. Thus, the bosses 66, 68 facilitate use of identical springs and identical adjusting members (having overlapping rims for effecting an interlock against reversing), while providing a full range of adjustability for the control device.

In order to provide sufficient strength in the overlapping rims of the adjusting members, rim thicknesses of approximately 0.10 inches have been provided in an actual working embodiment. Here, the distance d (FIG. 20), which corresponds with the minimum vertical staggering of the adjusting members, will also be approximately 0.10 inches. It is to be noted that this distance is equal to the difference between the distances which the bosses 66, 68 extend from the balance plate 46.

Adjusting member 84 includes a driving head 101 at its upper end, and adjusting member 86 includes an identically disposed driving head 103. As illustrated, the driving heads 101, 103 have external driving surfaces adapted for engagement with a wrench or similar driving tool. Application of a tool to the driving heads is facilitated by the overall configuration of the main housing and, particularly, the recess 18 defined thereby between the upper and lower sections 12, 14 thereof. In this regard, it is significant that the driving heads may be engaged from the side rather than from above.

As a practical matter, the electrical switching components at the upper end of the housing must be enclosed when the control device is installed. Since the driving heads of the adjusting members are disposed in recess 18 between the upper and lower sections 12, 14 of the main housing 10, it is possible to engage the heads from the side of the housing without removing the upper enclosure or otherwise disassembling any part of the control device.

A pair of lock rings 105, 107 are provided, each lock ring being disposed about one of the adjusting members 84, 86 in threaded engagement therewith.'- When springs 76, 78 have been adjusted to exert the proper biasing forces, the lock rings are threadably advanced into engagement with the top wall 96 of the housing. This will lock the adjusting members in position and cause the springs to be maintained in a desired condition of adjustment. Of course, when it is desired to change the spring adjustment, the lock rings are threadably moved away from engagement with the top cover of the housing to unlock the adjusting members. Movement of the lock rings is facilitated by knurled faces at the outer circumferences thereof.

The balance device 44 has a recessed seat 109 formed in the top surface thereof. Seat 109 is disposed immediately adjacent that sidewall of the balance plate which is located opposite the pivotal set of stops. Further, seat 109 is disposed approximately midway between the low and high pressure protrusions 52, 56. The lower end of an elongated actuating rod 111 is received in recessed seat 109 to couple the actuating rod with the balance plate. The actuating rod extends perpendicularly upwardly from the balance plate, through an opening 113 in the top wall 96 of the housing and, thence, entirely through the connecting section 16 and upper section 12 of the main housing 10. At its upper end, the actuating rod 111 is coupled with the electrical components of the control device.

Within the lower housing section there is included a compression coil spring 115 surrounding the actuating rod. As may be seen most readily in FTG. 3, one end of spring 115 is seated on the lower surface of the top wall 96 and the other end is directly coupled to the actuating rod 111. Spring 115 urges the actuating rod toward the balance plate creating a preload on the actuating rod which lessens variations in mechanical movements due to friction. This, in turn, improves accuracy and repeatability in the control functions.

Transducer Assembly and Bonnet Therefor Turning to the details of construction of the transducer assembly, and particularly the bonnet 22 thereof, it will be seen from the drawing that the end closure 24 of the bonnet has a stepwise, cylindrical configuration. At the lowermost end of the bonnet is a small diameter cylindrical portion 117 which defines the connecting port 40 of the control device. Immediately above portion 117 and in coaxial alignment therewith, is a cylindrical portion 119 of larger diameter. Portion 119 defines a cavity 121 within the bonnet. More specifically, however, cavity 121 is defined by a cylindrical side wall 123 and an annular bottom wall 124 within cylindrical portion 119 of the bonnet. The side wall 123 and bottom wall 124 join together to form a circular corner 125 at the lower end of the cavity 121. Connecting port 40 communicates with cavity 121 via an opening 127 in bottom wall 124.

A flange 129 extends radially outwardly from the uppermost part of the large cylindrical portion 119 of the bonnet end closure 24. The flange includes an upper annular surface 131 which, in the particular medium pressure transducer arrangement of FIGS. 2 and 3, en: gages diaphragm 32. The flange 129 also includes an inner, annular surface 133 which, in part, defines the aforesaid sensing chamber 38.

A pair of spaced annular recesses 135, 137 are disposed on the upper side of the flange 129 at either side of the upper annular surface 131. Annular recess 135, referred to as the first annular recess, is disposed radially outwardly of upper annular surface 131 and, preferably, opens into the outer surface 139 of the flange 129. Annular recess 137, referred to as the second annular recess, is disposed between upper annular surface 131 and inner annular surface 133.

The inner annular surface 133 is disposed at a level below that of the annular surface 131. Thus, in the assembled condition (wherein the device is adapted for sensing medium pressures as per FIGS. 2 and 3) the upper annular surface 131 engages the lower side 30 of the diaphragm 32, but the inner annular surface 133 does not. The clearance, therefore, between the inner annular surface 133 and the diaphragm 28 forms part of the sensing chamber 38.

Thebonnet ring 26 includes an inside shoulder 141 which, in the assembled condition, abuts part of the lower surface of the flange 129 of the bonnet end closure 24. The bonnet ring 26 also includes a plurality of radially outwardly projecting portions 143 each of which has a bore 145 therethrough. At the lower end of each bore 145 and concentric therewith, there is a counterbore 147. Preferably, the bonnet ring 26 will have four projecting portions 143, each of which'is radially spaced 90 froom the other. Cylinder member 36 includes a matching set of radially outwardly projecting portions 149 each of which has a bore 151 therethrough. In the assembled condition, bores 151 of the cylinder member are aligned with bores 145 of the bonnet ring.

A set of four eyelets 153 extend between the bonnet ring and the cylinder member 36, one eyelet passing through each pair of aligned bores 145, 151. Each eyelet 153, when formed into its final shape, has an upper head 155 tightly engaging the upper surface of the cylinder member and a lower head 157 tightly engaging a shoulder 156 between each bore 145 and counterbore 147. The eyelets secure cylinder member 36 (in the transducer arrangement of FIGS. 2 and 3) to the bonnet ring 26, and the cylinder member 36, in turn, clamps the bonnet end closure 24 against the upper annular surface 131 on the flange 129 of the bonnet. The clamping together of the bonnet ring, cylinder member and bonnet end closure serves to also clamp the dia phragm and O-ring with the bonnet.

Together, the bonnet ring, end closure, cylinder member, eyelets, O-ring and diaphragm are considered as the transducer assembly. The elements of the transducer assembly are independently held together, principally by the eyelets 153; that is, these elements are tightly held together by the eyelets regardless of whether the transducer assembly is secured to the main housing of the control device. The particular type of diaphragm and O-ring to be used in the transducer assembly and the precise manner of clamping the same therewithin will vary with the ranges of pressures to be sensed. This latter aspect of the invention will be described in more detail in a later section.

It will be apparent that, with the foregoing arrangement, different transducer assemblies may be interchanged with a minimum of time and effort. This interchangeability is important not only in adapting the control device to sense different ranges of pressures, but also in adapting the control device for use with a wide variety of different fluids. For instance, if highly corrosive fluids are involved, special materials will be required in the transducer assembly. Here, a special transducer assembly can be most readily coupled to a standard main housing which has standardcomponents therein.

Coupling Arrangement Between Transducer Assembly and Main Housing Turning to the details of the coupling arrangement between the transducer assembly and the lower section 14 of the main housing 10, there is provided a recessed area 159 around the bonnet ring 26 near the outer periphery of its upper face 161. A downwardly extending lip 163 on the lower section of the main housing fits within the recessed area 159 except in those parts of the bonnet ring where projecting portions 143 are dis posed (see FIGS. 9 and 10). Similarly, a set of upwardly extending lip members 165 on the bonnet 22 fit within a set of cooperating, spaced recesses 167 on the inside of the main housing adjacent the downwardly extending lip 163 (FIGS. 9 and 10).

The lower end of the lower housing section 14 also includes a set of outwardly projecting portions 169 corresponding to the projecting portions 143, 149 in the bonnet ring 26 and cylinder member 36, respectively. Each projecting portion 169 in the housing includes a threaded bore 171 therethrough. Each of the hollow eyelets 153 is aligned with one of the threaded bores 171 in the lower housing section, and a plurality of elongated screw members 173 pass through the eyelets and into the threaded bores 171 to connect the transducer assembly 20 to the housing. Thus, the interengagement of the lips 163 and lip members 165 with the corresponding recessed areas 159 and recesses 167 effects a proper fit and positioning of the transducer subassembly with respect to the housing.

By providing an arrangement wherein two entirely different sets of fasteners, namely, eyelets 153 and screw members 173, are disposed coaxially, one within the other, the overall construction of the transducer assembly is greatly simplified. Only one set of aligned projecting portions and bores are required in the bonnet ring and cylinder member to (a) independently secure the elements of the transducer assembly together (with eyelets 153), and (b) fasten the transducer assembly to the lower housing section of the control device (with screw members 173). Absent such as fastening arrangement, it would be far more difficult and costly to provide a control device with a detachable, interchangeable transducer assembly, the elements of which are independently secured together.

Lower Housing Section and Components Therein The interchangeability of the transducer assembly is further facilitated by the arrangement of elements within the lower housing section. As has already been made apparent a balance device 44 is guidably disposed within the inner space defined when guide member 49 and spacer ring 72 are clamped between upper and lower stop plates 62, 60. Together, the unit comprising this set of elements is referred to as the actuating unit. As previously mentioned, the actuating unit is independently secured in the housing, that is, even when the transducer assembly is detached from the lower section of the housing, the actuating unit and elements associated therewith will still be secured in place. It will be readily apparent that this greatly simplifies the operation of attaching and/or detaching a transducer assembly to and/or from the housing.

With regard to the independent fastening of elements within the lower housing section 14, it is to be noted that lower stop plate 60 includes a plurality of holes 175 passing therethrough, each hole having a countersink l77 associated with its lower end. (see FIG. 15). Preferably, there will be three holes 175 spaced 120 from one another. The plastic guide member 49, which overlies the upper stop plate, has a set of corresponding holes 179 therein, as does the upper stop plate (see holes 180, FIG. 11).

The lower housing section 14 has a stepwise cylindrical construction whereby an internal, inwardly extending, annular shoulder 181 is formed. The aforesaid actuating unit, in general, and the upper surface of the upper stop plate 62, in particular, rests against shoulder 181. A set of three equally spaced rib portions 183 extend radially inwardly from a part of the lower housing section above shoulder 181 (see FIGS. 3 and 7), The rib portions 183 each include a threaded hole 185, and each threaded hole is aligned with (a) one of the three holes in the upper stop plate 62, (b) one of the three holes 179 in guide member 49 and (c) one of the three holes 175 in the lower stop plate. Elongated fasteners 74 pass through the sets of aligned holes to threadably hold the actuating unit against the annular shoulder 181, thereby independently securing the same within the lower housing section.

Each screw fastener 74 includes a tapered head 187 (FIG. 3) which fits within the countersink 177 to hold the lower stop plate 60 in place. Most of the elements in the lower housing section 14 are arranged so as to ultimately react against the lower stop plate 60. Thus, the elements within the lower housing section may be considered to be retained therewithin by the lower stop plate 60 which, in turn, is held in place by the elongated screw fasteners 74.

At one side of the lower housing section 14,, there is a drain hole 189 with a plug 191 sealingly disposed therein. Removal of the plug opens the interior of the lower housing section 14 to communication with the exterior so that any accumulated liquids may be drained from the housing.

Connecting Section of the Housing As mentioned earlier, the main housing includes an offset connecting section 16 between its upper and lower sections 12, 14. The construction of the connecting section is best seen by reference to FIGS. 3 and 6 'of the drawing. As illustrated there, the connecting section is dominated by a vertically disposed, plate-like, center strut 191 integrally formed with and extending between the upper and lower housing sections l2, 14. A face plate 193, integrally formed with center strut 191, is disposed slightly behind the forwardmost edge (i.e., the radially inwardmost edge) of the center strut and is positioned perpendicularly with respect to the strut. Because the center strut 191 extends slightly forwardly of the face plate, it forms a forward vertical ridge 195 with respect thereto. Within the ridge 195 there is an elongated guide passageway 197 through which the actuating rod 111 extends.

A mounting plate 199, integrally formed with the center strut 191, is disposed slightly radially inwardly (i.e., forwardly) of the rearwardmost end 200 of the center strut in perpendicular relationship therewith. The mounting plate is disposed entirely radially outwardly of the outer circumference of the upper and lower housing sections 12, 14 and is positioned in spaced, parallel relationship with the face plate 193. Integral with the lower housing section 14 and mounting plate 199 is a horizontal plate 201 extending therebetween. The plate 201, in conjunction with the center strut 191, assures a strong and rigid union of the mounting plate with the housing. A pair of horizontal ribs, 202, 203, extending rearwardly of the mounting plate, further adds to the strength of the connecting section of the housing. It is to be observed that the lower of the two ribs, namely, rib 203, is aligned with the horizontal plate 201 and that the center strut 191 extends rearwardly of the mounting plate the same distance as do the horizontal ribs 202, 203. The mounting plate includes a pair of openings 205 disposed at the opposite lateral ends thereof and between the two horizontal ribs 203.

Adjacent the upper end of the connecting section 16 of the housing (i.e., the end which isjoined to the upper housing section 12) there is a horizontal cylindrical portion 207 integrally formed between the face plate 193 and the mounting plate 199. Cylindrical portion 207 includes a hollow cylindrical passageway 209 (FIG. 3) extending horizontally therethrough. At the opposite ends of cylindrical portion 207 are a pair of I (preferably by casting) as a unitary piece and that, in-

deed, the entire main housing 10, which consists of upper, lower, and connecting sections, is of a unitary cast construction.

Included on the connecting section 16 of the housing, at a position immediately to the rear of the adjusting members (as viewed in FIGS. 1 and 2), is an adjustment indicator 217 which has indicia thereon for providing readings of the values (in terms of percentages of the pressure range) atwhich the control points are set. Of course, the control points are set by adjusting the bias of each of the springs which act on the balance plate.

When the adjusting members 84, 86 are threadably moved into the positions shown in FIGS. 1 and 2, the maximum differential between control points is provided. In other words, the differential between control points will be of the full pressure range. In this instance, the low pressure control point, which typically will be the point at which the microswitch is deactuated, corresponds with the minimum pressure which can be sensed in the transducer assembly, and the high pressure control point, which typically will be the actuation point of a microswitch, corresponds with the maximum pressure can be sensed in the particular transducer assembly shown in FIGS. 1 and 2.

As described above, the adjusting members are vertically staggered even when the springs 76, 78 are adjusted to exert equal, or nearly equal biases. To compensate for this vertical staggering, the indicia lines for each value on adjustment indicator 217 are similarly staggered. Thus, in viewing FIGS. 1 and 2, it will be seen that the 0% indicia line (which indicates that a spring adjustment whereby one of the two control points is set at 0% of the pressure range) is higher on the left-hand side, adjacent adjusting member 84 than it is on the right-hand side, adjacent the adjusting member 86. The same is true with regard to the other indicia.

Upper Housing Section and Components Associated Therewith Integrally formed with the connecting portion 16 of the housing and, more specifically, with the center strut 191 and face plate 193 thereof, is the upper housing section 12. This section includes a bottom wall 219 and an annular side wall 221 extending upwardlyfrom the bottom wall. As best seen in FIGS. 3 and 5, a pair of diametrically opposed, semicircular segments 223 extend slightly inwardly from the side wall 221. Segments 223 are drilled and tapped so that a bracket 225 can be mounted thereon by screw fasteners 227, 228. Nuts 229, threadably disposed on screw fastener 227, facilitate adjustment of the bracket height. As best seen in FIG. 3, the bracket 225 is mounted to span the area between the segments 223 of the upper housing section.

A control means preferably in the form of a conventional microswitch 231 is secured above the lower housing portion by bracket 225. Other types of electrical switches or fluid controlling valves may be used in place of a microswitch.

In the illustrated embodiment, the microswitch includes a casing 233, and an actuating button 236 extending therefrom. Also, there is an insulating barrier 238, which surrounds casing 233. Microswitch 231 has two distinct, mutually cancelling control modes corresponding to two distinct actuation positions of the actuating button 236. Preferably, but by way of example only, these two positions and the corresponding control modes are referred to, respectively, as the actuation" or on position or control mode, and the deactuation or off position or control mode. Ofcourse, and inherent displacement differential exists between the two control positions.

As indicated earlier, guide passageway 197 for the actuating rod 111 extends from the opening 113 in the top wall 96 of the lower housing section and continues along through the ridge 195 in the connecting section of the housingv From here, the guide passageway 197 extends upwardly through the bottom wall of the upper housing section and thence through an upwardly extending base 240 disposed above the bottom wall 219. The guide passageway 197 then opens into the space defined by the annularly shaped side wall 221 of the upper housing section.

The actuating rod 111 extends entirely through the guide passageway 197 so that its upper end is disposed above the base 240 but below the actuating button 236 of the microswitch 231. A resilient element, preferably a coil spring 242, extends between the upper end of the actuating rod 111 and the actuating button 236 to resiliently couple the actuating rod to the microswitch. Spring 242 is sufficiently weak to serve as a lost motion connection between the rod 111 and button 236, that is, by virtue of spring 242, there is a displacement reduction as the motion of the actuating rod is transferred to the actuating button. Because the overall range of vertical displacement of the diaphragm 32, piston 42, balance device 44 and actuating rod 111 is substantially greater than that of the actuating button 236 of the microswitch, it is necessary to compensate for the different displacement ranges. Here, the spring 242 provides a simple and inexpensive means for doing As illustrated in FIG. 4, a simple and easily detachable connection between the spring 242 and the push button is achieved by providing, on the upper end of the spring a hollow member 244 with a flared end 246 which mates with the chamfered end of the actuating button 236.

As shown in FIGS. 1 and 2, a cover 248 encloses both the upwardly facing portions of the upper housing section 12 as well as the microswitch 231 mounted thereon. Cover 248 is of a light, rather. resilient construction. It may be readily snapped into" place about the side wall 221 by virtue of cooperating dentent elements 249, 250, respectively, on the cover and side wall. Alternatively, and as shown in FIG. 3, an explosionproof cover 252 may enclose the microswitch. Here, the cover is secured in place by cooperating threads between the inside of the cover and the outside of the side wall 221. A driving head 253 is provided at the top of cover 252 to facilitate installation and removal of the cover. Also, a gasket 254 is interposed between the cover and upper housing section 12 to provide a tightly sealed enclosure.

Arrangement of Transducer Assembly for Sensing Different Ranges of Pressures A mentioned earlier, the particular arrangement of elements in the transducer assembly may vary according to the ranges of pressures to be sensed. Preferably, three different transducer arrangements are provided to cover an extremely wide range of different applications.

The details of construction of the bonnet 22 (i.e., the combined end closure 24 and ring 26) of the transducer subassembly have been described in a preceding section. As will be brought out more fully hereinafter, a single bonnet construction serves for all the different arrangements of the transducer assembly. Because of this, significant economies are effected.

The general discussion, in a preceding section, of the construction of the transducer assembly has been with regard to the arrangement for sensing medium pressures as illustrated in FIGS. 2, 3, 18 and 19. In this arrangement, there is included a cylinder member 36, illustrated separately in FIG. 16, having a cylindrical opening 260 which may be of various different sizes. Selection of one particular opening size will depend on the precise range of intermediate pressures to be sensed. In practice, size selections of approximately 0.57 inches, 0.80 inches and 1.13 inches in the diameter of the cylindrical opening 260 have been found to be best for intermediate ranges of pressures. Of course, the larger of the foregoing size selections are used for sensing the lower ranges of intermediate pressures, and vice versa.

As described above, cylinder member 36 includes a set of four equally spaced projecting portions 149 disposed outwardly of the circumference 262 thereof. An eyelet 153 passes through a bore 151 in each projecting portion to secure the cylinder member to the bonnet 22. When the cylinder member is thus secured, its outer circumference 262 will be disposed in close fitting relationship with the inside surfaces of the upwardly extending lip members 165 of the bonnet (see FIG. 8).

The O-ring 28 of intermediate diameter is disposed in the second annular recess 137 when the transducer assembly is arranged for sensing intermediate ranges of pressure, i.e., when the assembly is arranged as per FIGS. 2, 3, 18 and 19. In this instance, the first annular recess remains unused.

As previously indicated, diaphragm 32, disposed between the O-ring 28 and cylinder member 36, is resiliently urged by the O-ring into sealing engagement with the cylinder member. The O-ring also serves to seal the diaphragm with respect to the bonnet, whereby the bonnet, the diaphragm, and the O-ring define a medium pressure sensing chamber 38 therebetween. Together, the cylinder member 36, diaphragm 32 and O- ring 28 are to be considered as the medium pressure sensing device of the transducer assembly as arranged for sensing medium pressures. Because the O-ring of the sensing device mates with and is positioned by the second annular recess 137, this recess is to be considered an element for coupling the medium pressure sensing device with the bonnet.

As will be apparent from FIGS. 2, 3, l8 and 19, the medium pressure sensing chamber 38 includes both the cavity 121 in the bonnet as well as the space 264 between the upper surface of the flange 129 and the diaphragm 32. In this instance, the upper annular surface 131 on the flange of the bonnet engages the lower side 30 of the diaphragm.

As an element separate from the transducer assembly, a medium pressure piston 42 is displaceably disposed within the cylindrical opening 260 in cylinder member 36. The medium pressure piston 42 has a diameter slightly less than that of the cylindrical opening, and, as with the pistons 42 may be provided to adapt the control device to specific ranges of intermediate pressures. Preferably, pistons having diameters of approximately 0.56, 0.79 and l.l2 inches are provided to correspond with the foregoing preferred size selections for cylindrical opening 260.

In the low pressure arrangement illustrated by FIG. 9, the transducer assembly includes a low pressure cylinder member 36 (illustrated separately in FIG. 17) which has a large cylindrical opening 266 (FIG. 17). The size of cylindrical opening 266 will vary, depending on the particular low pressure application intended. Preferably, selection of a particular size may be made from two different versions of cylinder member 36, one having an opening 266 which is approximately 1.46 inches in diameter, and the other having an opening which is approximately 2.06 inches in diameter. Of course, the cylinder member having the larger opening is used in applications where the very lowest range of pressures is to be sensed, and the cylinder member having the smaller opening is used for sensing a higher range of pressures which still falls within the overall low pressure ranges for which the low pressure cylinder member 36' is intended.

A extending radially outwardly from the circumference of cylinder member 36', each include a bore passing therethrough. As previously described in connection with medium pressure cylinder member 36, an eyelet I53 passes through each bore to clamp the cylinder member 36 to the bonnet 22 and to hold the elements of the transducer assembly together.

To accommodate the large cylindrical opening 260, the low pressure cylinder member 36 must have an outside diameter which is larger than that of the medium pressure cylinder member 36. Accordingly, the circumference 268 of the low pressure cylinder member 36 is disposed outwardly of the upwardly extending lip members 165 of the bonnet. To prevent interference with the lip members, a set of four inwardly extending slots 270 are provided at the outside of the cylinder member 36', and the upwardly extending lip members 165 fit within these slots when the cylinder member is secured to the bonnet 22.

In the present instance, where the transducer assembly is arranged for sensing low pressure, a large diameter O-ring 28' is disposed in the first annular recess 135 of the bonnet 22, and, as shown in FIG. 9, the second annular recess 137 remains unused. Diaphragm 32 is disposed between the O-ring 28' and the cylinder member 36. The O-ring resiliently presses the diaphragm against the cylinder member thereby sealing the diaphragm with respect to the bonnet and cylinder member. Thus, a low pressure sensing chamber 38 is defined between the bonnet, the diaphragm 32, and the O-ring 28. Together, cylinder member 36, diaphragm 32 and O-ring 28 are to be considered as the sensing device of the transducer assembly as arranged for sensing'low pressures. Because the O-ring of the sensing device mates with and is positioned by the second annular recess 135, this recess is to be considered as an element for coupling the low pressure sensing device with the bonnet.

It will be readily apparent from FIG. 9 that the low pressure sensing chamber 38' includes both the cavity 121 in the bonnet as well as the space 264 between the upper surface of the flange 129 and the diaphragm. When the transducer assembly is arranged for sensing low pressures, the upper annular surface 131 of the bonnet is exposed to the sensing chamber 38'. Here, this surface does not engage another element as it does in the medium and high pressure arrangements.

A low pressure piston 42', which is not to beconsidered part of the transducer assembly per se, is displaceably disposed within the large cylindrical opening 266. The size of the low pressure piston 42 may vary depending on the size selection for the cylindrical opening 266. The piston will be sized slightly smaller than the cylindrical opening and will preferably have a diameter of approximately either 1.45 or 2.05 inches, these sizes corresponding, respectively, with the preferred diameters of either 1.46 or 2.06 inches for the cylindrical opening 266.

When the transducer assembly is arranged for sensing high pressures, as illustrated in FIG. 10, a two-part, high pressure cylinder member 36" is provided. The first part 274 of cylinder member 36 is of generally the same configuration as medium pressure cylinder member 36, but its central opening 276 is much smaller than the cylindrical opening 260 of cylinder member 36. Preferably, the central opening 276 has a diameter of approximately 0.31 inches. As with the medium pressure cylinder member 36, the first part 274 of high pressure cylinder member 36" includes a set of projecting portions 149" having bores 151" therein. Eyelets 153, passing through each of the bores 151 secure the first part 274 directly to the bonnet.

The second part 278 of high pressure cylinder member 36" has a hollow cylindrical configuration with a cylindrical bore 280 running axially therethrough. The second part is disposed in cavity 121 above a small diameter diaphragm 32" and a small diameter O-ring 28". The O-ring 28" is disposed in the corner formed between the cylindrical side wall 123 and annular bottom wall 124 of the cavity 121. O-ring 28" resiliently urges the diaphragm 32 against an annular face 286 at the lower end of the second part 278 of the high pressure cylinder member 36". The O-ring 32" serves to seal the diaphragm with respect to both the cylinder member 36" and also with respect to the bonnet 22, whereby a high pressure sensing chamber 38" is defined between the bonnet 22, the diaphragm 32" and the O-ring 28".

The cylindrical bore 280 of the second part 278 of the cylinder member 36" includes a counterbore 290 at its upper end. A high pressure piston 42" which is disposed within the cylindrical bore 280, has an annular ridge 294 thereon, the ridge 294 being disposed within the counterbore 290. The first part 274 of the cylinder member directly engages a face 296 at the upper end of the second part 278 to retain the second part within the transducer assembly. In addition, the first part 274 retains the high pressure piston 42" within the cylindrical bore by partially enclosing the counterbore 290. This prevents movement of the annular ridge 294 of the piston out of the counterbore.

In the high pressure arrangement, annular recesses 135 and 137 both remain unused. Again, the cylinder member (in this instance, the lower part 278 thereof), the diaphragm 32" and the O-ring 28" are to be considered, in combination, as the sensing device of the transducer assembly. Here, however, the piston 42 is retained within the transducer assembly as an element thereof. Therefore, in this high pressure arrangement only, the piston may also be considered part of the sensing device of the transducer assembly. Because the O-ring 28" of the sensing device mates with and is positioned by the corner 125 of cavity 121, this comer is considered as an element for coupling the high pressure sensing device with the bonnet.

In the high pressure arrangement of FIG. 10, the cylindrical bore 280 of the second part 278 of the cylinder member 36 may be of various different sizes. Selection of one particular size will depend on the precise range of high pressures to be sensed. In practice, size selections of approximately 0.2 l 0.30 and 0.36 inches in the diameter of cylindrical bore 280 are provided. With these size selections, piston size selections of approximately O.20, 0.29 and 0.35 inches in diameter, respectively, are also provided.

The counterbore 290, in the second part 278 of cylinder member 36", and the annular ridge 294 on piston 292 are, of course, larger in diameter than any of the foregoing possible diameters for cylindrical bore 280 or piston 292. Preferably the diameters of counterbore 290 and annular ridge 294 are approximately 0.47 and 0.45 inches, respectively, regardless of the sizes of cylindrical bore 280 and piston 42". However, another, larger size selection for the cylindrical bore 280 and piston 42 is provided in addition to the foregoing size selections. Here, the cylindrical bore has a diameter of approximately 0.47 inches and the piston has a diameter of approximately 0.46 inches. In this instance there is no need for a counterbore nor for an annular ridge to retain the piston with the cylindrical bore, and, accordingly, these are eliminated (elimination of counterbore and annular ridge not shown). The first part 274 of the cylinder member 36" will still perform its retaining function, as described above, but, in this case, it directly retains the piston itself rather than the annular ridge 294 thereof.

High pressure piston 42, in all of its sizes, includes an upward extension 298. This extension passes through the central opening 276 in the first part 274 of cylinder member 36 and engages the ball 70 of the balance device 44 to couple the piston to the balance device. Of course, in the transducer arrangements for sensing low and medium ranges of pressures, the piston (42' or 42) is coupled to the balance device 44 by direct engagement of the piston with the ball 70.

Operation The operation of the control device of the present invention will be described below, with reference being made to FIGS. 2, l9 and 20 showing various displaceable elements in different sequential positions. While reference is had only to figures illustrating a transducer assembly arranged for sensing medium pressures, it will be understood that the operation is basically the same when other transducer arrangements are used.

FIG. 18 illustrates the extreme low pressure position of the diaphragm 32, piston 42, and balance device 44. In this position, the lower pivotal protrusion 51, low pressure protrusion 52 and rest protrusion 58 are held at rest against the lower stop plate 60 by the force of the coil springs 76, 78. High pressure protrusion 56 is at a position spaced from the upper stop plate 62. As pressure in sensing chamber 38 increases, the diaphragm 32 will be displaced upwardly. This upward displacement will be transmitted to the piston 42 and thence to the ball of the balance device 44. The balance device will first begin to move against the force of the weaker of the two coil springs, namely, spring 76 lifting rest protrusion 58 from the lower stop plate 60. Meanwhile, the high pressure spring 78 will maintain the lower pivotal protrusion 51 and low pressure protrusion 52 firmly in place against the lower stop plate 60. The above-described movement of the balance plate, therefore, as viewed in the drawing, is a clockwise pivotal movement about axis A (defined by the points of contact of protrusions 51 and 52 with the lower stop plate 60.

Pivotal movement of the balance device about the axis A will continue until the high pressure protrusion 56 comes into contact with the upper stop plate 62 to restrain further upward movement. At this point the balance plate is disposed in the middle position as illustrated in FIG. 19. The balance plate will remain in this position until the pressure in the chamber 38 has increased an amount sufficient to overcome the bias of the high pressure spring 78. At this point, the low pressure protrusion 52 is lifted from the lower stop plate 60 and moves upwardly. To permit such movement, the balance plate pivots in a counterclockwise direction about the axis B (defined by the points of contact of upper pivotal protrusion 54 and high pressure protrusion 56 with the upper stop plate 62). Pivotal move ment of the balance plate about axis B will continue until the extreme high pressure position shown in FIG. 2 is reached.

Upon decrease in pressure, the sequence of operations is precisely the reverse of that described above. With reference to FIGS. 2 and 19, the pivotal movement about axis B from the high pressure position of FIG. 2 to the middle position of FIG. 19, as pressure decreases, is in a clockwise direction. After a decrease in pressure to a point at which the weaker spring 76 is able to overcome the upward force on the diaphragm, the balance device will begin to return from the middle position of FIG. 19 toward the low pressure position of FIG. 18, pivoting in a counterclockwise direction about the axis A.

It will be understood that, at all times when the balance device pivots about the axis A, the line of force of the high pressure spring 78 will be acting directly through that axis, so that the high pressure spring is rendered ineffective, exerting no influence on the pivotal movement of the balance device. Likewise, during movement of the balance device about the axis B, the low pressure spring 76 acts directly through that axis and is rendered ineffective, exerting no influence on the pivotal movement.

The balance device is guided in its alternating pivotal movement by the prism-shaped guide opening 50 in the guide member 49. As described earlier, the prismshaped guide projection 48 of the balance device is displaceably disposed within guide opening 50 in tight fitting relationship therewith. The particular positioning and configuration of the guide opening and guide projection are such as to (a) minimize resistance to pivotal movement, (b) prevent binding of the balance device within the guide opening, and, (c) at the same time, provide an effective guiding of the balance device.

it will be readily apparent from FIG. 7 of the drawing that side 48a of guide projection 48 is parallel to axis A, and, likewise, side 4819 is parallel to axis B. Thus, all points falling on a line (in the plane of the balance plate) corresponding with side 48a are disposed an equal distance from the axis A and all points falling on a line (in the plane of the balance plate) corresponding with side 48b are disposed an equal distance from the axis B. Moreover, all points falling on the line corresponding with side 48a are disposed further from axis A than are any other points on the guide projection 48. Likewise, all points falling on the line corresponding with side 48b are disposed further from axis B than are any other points on the guide projection.

When the balance device pivots about either axis, the guide projection moves generally vertically yet through a slight are. It will be readily apparent that the magnitude of vertical displacement of the guide projection 48 will be greatest at the points thereon disposed furthest from the axis about which pivotal movement is taking place. Thus, when the balance device pivots about axis A, the points falling on a line corresponding with side 48a of the guide projection will move vertically more than any other points thereon. The same is true of the points falling on a line corresponding with side 4812 when the balance device pivots about axis B. It will also be apparent, however, that the points on the guide projection 48 which go through the greatest vertical displacement during pivoting of the balance device are also the points where the arcuate movement is most pronounced.

With regard to the cooperating, interfitting guide projection 48 and guide opening 50, large arcuate movements of the balance device could cause excessive friction and resistance between the guide projection and guide opening and might even cause binding thereof. The configuration of the guide projection and its positioning with respect to the balance plate 46 brings those points on the guide projection which are furthest from each axis relatively close to each axis. Thus, in practice, while the center of the guide projection is disposed approximately 0.44 inches from axes A and B, side 48a, which defines the points on the guide projection furthest from axis A, is disposed only about 0.59 inches therefrom. Side 4812, which defines the points on the guide projection furthest from axis B, is disposed approximately the same distance (0.59 inches) therefrom. Notwithstanding the foregoing, the guide projection has a relatively large perimeter (approximately 1 .69 inches in an actual device) to provide an effective guiding action for the balance device.

Providing a guide projection wherein the furthest points thereon from each axis are still relatively close to each axis minimizes the undesireable effects which might result from exaggerated arcuate movements at substantial distances from each axis. That is, the positioning and configuration of the guide projection 48 helps to minimize friction and resistance between the guide projection and guide opening and helps prevent binding therebetween.

Although the side of the guide projection opposite each axis is relatively close thereto, each such side is still not so close to the axis as to render insignificant the vertical component of movement in the region of each such side. In fact, the configuration of the guide projection and the positioning thereof with respect to the balance plate 46 is such that the combined area of the guiding surfaces (i.e., sides 48a, 48b and 480 in cooperation with guide opening 50) will be maximized in the region of greatest vertical movement of the guide projection to thereby enhance the guiding effect. More specifically, when the balance device pivots about axis A, more than two-thirds of the guiding surface area of the guide projection is disposed beyond a line passing through the center of the guide projection and parallel to axis A. An analogous relationship exists with respect to axis B. The large proportion of guide surface area beyond the above-defined lines enhances the guiding effect, yet the maximum distance which the guide member extends beyond such lines is, in each case, less than one third of the distance between the axis and the points on the guide member disposed furthest therefrom. As described previously, this last-mentioned feature, namely, the overall closeness of the guide member to both axes, minimizes any undesirable effects of arcuate movement of the guide member with respect to the guide opening.

The above-described alternate pivotal movements of the balance device effect only a linear displacement of the actuating rod 111. The motion is transmitted from the balance device to the actuating rod 111 and thence to the spring 242 which serves as a lost motion connection with the actuating button 236 of the microswitch 231. The vertical position of the microswitch 231 with respect to the housing 10 is adjusted so that the middle position of the balance device, as illustrated in FlG. l9, corresponds to the middle position in the inherent displacement differential of the microswitch. In other words, with the balance device in its middle position, the microswitch actuating button is midway between the control points. Assuming that the deactuation or off point of the microswitch corresponds to the vertically lower actuation button position in relation to the on point, and further assuming that the balance device 44 is in the low pressure position of FIG. 18, and that the microswitch is in the off position, as pressure increases in the chamber 38, the balance device pivots about the axis A until reaching the middle position of FIG. 20. With a sufficient additional increase in pressure, the balance plate then begins to pivot about axis B. During this latter pivotal movement, the rod 111 will cause the button 236 to pass through its actuation position shifting the switch into the on control mode. As described above, a pressure decrease causes the balance plate to move back to the middle position by pivoting about axis B. Then, after sufficient additional decrease in pressure, the balance plate begins to pivot about axis A toward the low pressure position. During this latter pivotal movement about axis A, rod 111 causes the button 236 to pass through the deactuation position moving the switch into the off control mode.

While throughout the above description words such as vertical, upper, lower, forward, rear,

right" and left have been used,it will be understood that these terms are used only to describe relative relationships and are not intended to be limiting. It will also be understood that those skilled in the art may make many changes and modifications to the abovedescribed embodiments of the present invention without departing from the spirit and scope thereof.

What is claimed is:

1. A control device comprising:

a. a housing;

b. a chamber in said housing;

c. a sensing means defining at least part of said chamber, said sensing means being displaceable through a stroke;

d. a balance means, said sensing means being operatively connected to said balance means;

e. a pair of bosses on one side of said balance means, one boss extending a greater distance from said one side than the other boss;

f. stop means cooperating with said balance means defining a pair of axes about which said balance means pivots;

g. first and second biasing means each of which is connected with one of said bosses;

h. adjusting means coupled with said biasing means, said adjusting means including an interlock means preventing said first biasing means from being adjusted to exert a biasing force greater than that of said second biasing means,

i. a control means operatively coupled to said bal ance means, said control means including means shiftable between two control modes;

j. whereby displacement of said sensing means through one part of its stroke effects both pivoting of said balance means about said first axis and shifting of said control means into one mode, and movement of said sensing means through another part of its stroke effects both pivoting of said balance means about the other axis and shifting of said control means into the other mode, whereby adjustment of said biasing means effects independent adjustment of said control modes, and whereby said bosses facilitate full adjustability of said biasing means and control modes.

2. A control device as defined in claim 1, wherein said first biasing means is substantially identical to said second biasing means.

3. A control device as defined in claim 2, wherein each biasing means is a coil spring held in compression.

4. A control device as defined in claim 1, wherein said adjusting means includes a pair of identical adjusting members.

5. A control device as defined in claim 4, wherein said interlock means includes a pair of overlapping rims. each rim being disposed on one of said adjusting members.

6. A control device as defined in claim 1, wherein said control means is a microswitch.

7. A control device as defined in claim 1, wherein each of said bosses are integral with said balance means.

8. A control device as defined in claim 1, wherein each of said bosses includes a convex portion.

9. A control device defined in claim 8, including a spring retainer coupled to one end of each biasing means, each spring retainer having a concave recess therein.

10. A control device defined in claim 9, wherein said convex portion of each boss engages said concave recess of one of said retainer members.

11. A control device defined in claim 1:

a. wherein said stop means include pluralities of convex protrusions on said balance means and also include upper and lower stop plates disposed, respectively, above and below said balance means;

b. including guide means, said guide means including a guide projection on said balance means;

0. said bosses, said guide projection, and said convex protrusions of said stop means being of the same material as said balance means and being integral therewith.

12. A control device as defined in claim 11, wherein said balance means, said bosses, said guide projection, and said convex protrusions of said stop means are formed as a unitary piece composed of molded plastic material.

13. A control device as defined in claim 12, including, on said guide projection, a means for connecting said sensing means with said balance means, said connecting means including a bearing member of harder material than the material of said balance means, said bearing member being molded into said balance means.

14. A control device comprising:

a. a housing;

b. a chamber in said housing;

0. a sensing means defining at least part of said chamber, said sensing means being displaceable through a stroke;

(1. a balance means, said sensing means being operatively connected to said balance means;

e. stop means cooperating with said balance means defining a pair of axes about which said balance means pivots;

f. a means for guiding said balance means, said guiding means including a guide projection on said balance means and a guide member in said housing, said guide member including a guide opening within which said guide projection is displaceably disposed;

g. said guide projection having substantially the configuration of a prism with triangular end faces, said guide opening having a configuration corresponding to that of said guide projection.

15. A control device comprising:

a. a housing;

b. actuating means in said housing;

c. a transducer connected to said housing at one end thereof;

d. a chamber in said transducer and a displaceable sensing device in said transducer defining at least part of said chamber, said sensing device being coupled to said actuating means;

e. said sensing device including a diaphragm;

f. a cylinder member engaging said diaphragm;

g. means extending between said transducer and said housing for detachably securing said transducer to said housing;

h. holding means in said transducer for holding said sensing device therein when said transducer is detached from said housing, said holding means including a plurality of separate, hollow, tubular eyelets extending through outwardly disposed bores in said cylinder member, said extending means extending through said eyelets; and

i. a control means operatively connected with said actuating means.

16. A control device as defined in claim 15 wherein said control means is a microswitch.

17. A control device as defined in claim 15, wherein said means extending between said transducer and said housing are a plurality of elongated members, each elongated member extending through one of said eyelets.

18. A control device comprising:

a. an upper enclosure and a lower enclosure, said upper and lower enclosures being vertically spaced from each other and being connected together by a connecting section;

b. biasing means in said lower enclosure;

c. pressure sensing means coupled with said biasing means;

d. switch means in said upper enclosure, said switch means being coupled to said pressure sensing means;

e. adjusting means coupled to said biasing means, part of the adjusting means extending from the lower enclosure into the space between both enclosure and being external to both enclosures;

f. whereby said control device may be readily adjusted from the exterior thereof.

19. A control device as defined in claim 24, wherein said switch means is a microswitch.

20. A control device as defined in claim 18:

a. further including a balance means in said lower enclosure and a plurality of stop means in said lower enclosure, said stop means cooperating with said balance means defining a pair of axes about which said balance means pivots, said biasing means'comprising a pair of springs, at least one of which being adjustable, said pair of springs being coupled with said balance means;

b. said adjusting means being coupled with at least one spring of said pair; and

c. an actuating rod extending between said balance means in said lower enclosure and said switch means in said upper enclosure.

21. A control device as defined in claim 20, wherein said adjusting means includes at least one elongated, hollow, adjusting member enclosing the major portion of at least one spring of said pair in all positions of adjustment to thereby guide said biasing means and prevent buckling thereof.

22. A control device as defined in claim 21, wherein said adjusting means includes a pair of said adjusting members, each adjusting member of said pair enclosing one of said springs. 

1. A control device comprising: a. a housing; b. a chamber in said housing; c. a sensing means defining at least part of said chamber, said sensing means being displaceable through a stroke; d. a balance means, said sensing means being operatively connected to said balance means; e. a pair of bosses on one side of said balance means, one boss extending a greater distance from said one side than the other boss; f. stop means cooperating with said balance means defining a pair of axes about which said balance means pivots; g. first and second biasing means each of which is connected with one of said bosses; h. adjusting means coupled with said biasing means, said adjusting means including an interlock means preventing said first biasing means from being adjusted to exert a biasing force greater than that of said second biasing means, i. a control means operatively coupled to said balance means, said control means including means shiftable between two control modes; j. whereby displacement of said sensing means through one part of its stroke effects both pivoting of said balance means about said first axis and shifting of said control means into one mode, and movement of said sensing means through another part of its stroke effects both pivoting of said balance means about the other axis and shifting of said control means into the other mode, whereby adjustment of said biasing means effects independent adjustment of said control modes, and whereby said bosses facilitate full adjustability of said biasing means and control modes.
 2. A control device as defined in claim 1, wherein said first biasing means is substantially identical to said second biasing means.
 3. A control device as defined in claim 2, wherein each biasing means is a coil spring held in compression.
 4. A control device as defined in claim 1, wherein said adjusting means includes a pair of identical adjusting members.
 5. A control device as defined in claim 4, wherein said interlock means includes a pair of overlapping rims, each rim being disposed on one of said adjusting members.
 6. A control device as defined in claim 1, wherein said control means is a microswitch.
 7. A control device as defined in claim 1, wherein each of said bosses are integral with said balance means.
 8. A control device as defined in claim 1, wherein each of said bosses includes a convex portion.
 9. A control device as defined in claim 8, including a spring retainer coupled to one end of each biasing means, each spring retainer having a concave recess therein.
 10. A control device as defined in claim 9, wherein said convex portion of each boss engages said concave recess of one of said retainer members.
 11. A control device as defined in claim 1: a. wherein said stop means include pluralities of convex protrusions on said balance means and also include upper and lower stop plates disposed, respectively, above and below said balance means; b. Including guide means, said guide means including a guide projection on said balance means; c. said bosses, said guide projection, and said convex protrusions of said stop means being of the same material as said balance means and being integral therewith.
 12. A control device as defined in claim 11, wherein said balance means, said bosses, said guide projection, and said convex protrusions of said stop means are formed as a unitary piece composed of molded plastic material.
 13. A control device as defined in claim 12, including, on said guide projection, a means for connecting said sensing means with said balance means, said connecting means including a bearing member of harder material than the material of said balance means, said bearing member being molded into said balance means.
 14. A control device comprising: a. a housing; b. a chamber in said housing; c. a sensing means defining at least part of said chamber, said sensing means being displaceable through a stroke; d. a balance means, said sensing means being operatively connected to said balance means; e. stop means cooperating with said balance means defining a pair of axes about which said balance means pivots; f. a means for guiding said balance means, said guiding means including a guide projection on said balance means and a guide member in said housing, said guide member including a guide opening within which said guide projection is displaceably disposed; g. said guide projection having substantially the configuration of a prism with triangular end faces, said guide opening having a configuration corresponding to that of said guide projection.
 15. A control device comprising: a. a housing; b. actuating means in said housing; c. a transducer connected to said housing at one end thereof; d. a chamber in said transducer and a displaceable sensing device in said transducer defining at least part of said chamber, said sensing device being coupled to said actuating means; e. said sensing device including a diaphragm; f. a cylinder member engaging said diaphragm; g. means extending between said transducer and said housing for detachably securing said transducer to said housing; h. holding means in said transducer for holding said sensing device therein when said transducer is detached from said housing, said holding means including a plurality of separate, hollow, tubular eyelets extending through outwardly disposed bores in said cylinder member, said extending means extending through said eyelets; and i. a control means operatively connected with said actuating means.
 16. A control device as defined in claim 15 wherein said control means is a microswitch.
 17. A control device as defined in claim 15, wherein said means extending between said transducer and said housing are a plurality of elongated members, each elongated member extending through one of said eyelets.
 18. A control device comprising: a. an upper enclosure and a lower enclosure, said upper and lower enclosures being vertically spaced from each other and being connected together by a connecting section; b. biasing means in said lower enclosure; c. pressure sensing means coupled with said biasing means; d. switch means in said upper enclosure, said switch means being coupled to said pressure sensing means; e. adjusting means coupled to said biasing means, part of the adjusting means extending from the lower enclosure into the space between both enclosure and being external to both enclosures; f. whereby said control device may be readily adjusted from the exterior thereof.
 19. A control device as defined in claim 24, wherein said switch means is a microswitch.
 20. A control device as defined in claim 18: a. further including a balance means in said lower enclosure and a plurality of stop means in said lower enclosure, said stop means cooperating with said balance means defining a pair of axes aboUt which said balance means pivots, said biasing means comprising a pair of springs, at least one of which being adjustable, said pair of springs being coupled with said balance means; b. said adjusting means being coupled with at least one spring of said pair; and c. an actuating rod extending between said balance means in said lower enclosure and said switch means in said upper enclosure.
 21. A control device as defined in claim 20, wherein said adjusting means includes at least one elongated, hollow, adjusting member enclosing the major portion of at least one spring of said pair in all positions of adjustment to thereby guide said biasing means and prevent buckling thereof.
 22. A control device as defined in claim 21, wherein said adjusting means includes a pair of said adjusting members, each adjusting member of said pair enclosing one of said springs. 